The present invention relates to an electron beam diffraction measuring apparatus which applies an electron beam to a measuring object in a vacuum and examines its crystal structure on the basis of the intensity distribution of the electron beam diffracted by the measuring object. More particularly, the invention pertains to an electron beam diffraction measuring apparatus for scrutinizing the crystal structure of the measuring object by removing inelastic scattering. components of the diffracted electron beam.
FIG. 1 is a diagrammatic showing of a conventional electron beam diffraction measuring apparatus. The measuring apparatus in its entirety is placed in a vacuum. An electron beam 2 emitted from an electron gun 1 strikes on a measuring object 3 on a specimen table 20 and is scattered. At this time, the intensity distribution of scattered electrons is dependent on the energy of the electron beam 2 and the crystal structure of the measuring object 3--this phenomenon is called diffraction. On a fluorescent screen 4 disposed in the direction of diffracted electron beams 5 a pattern appears in accordance with the intensity distribution of the diffracted electron beams which corresponds to the crystal structure of the measuring object 3 (see FIG. 3, for instance). This pattern can be used to examine the crystal structure of the measuring object 3.
FIG. 2 is a schematic representation of another prior art example of electron beam diffraction measuring apparatus, which directly measures the intensity distribution of the diffracted electron beams 5 by means of an electron beam detector 6 instead of using the fluorescent screen 4 in FIG. 1. The intensity distribution of the diffracted electron beams 5 can be obtained by measuring the electron beam intensity while at the same time moving the electron beam detector 6 in a direction of a radius vector the rotating center of which is at the point of diffraction P on the specimen 3 by means of a driver not shown (i.e. turning the detector 6 around the point of diffraction P over an arcuate distance covering all the diffracted electron beams 5). FIG. 3 is a graph showing an example of the diffracted electron beam intensity distribution measured by the above method. The diffracted electron beam intensity distribution has maximal values in directions of plural diffraction angles .alpha. which are determined by conditions of diffraction, that is, the lattice plane and lattice constant of the measuring object 3, the angle of incidence .theta. of the electron beam 2 to the measuring object 3 and the energy of the electron beam 2 (an electron acceleration voltage eV or the wavelength of the electron beam 2). In this instance, the diffracted electron beam intensity does not become zero either at places other than those of the diffraction angles .theta. where the diffracted electron beam intensity has maximal values. This is because of the presence of inelastic scattering or multiple scattering components which are usually regarded as background components. When the measuring object is a material close to a perfect crystal, a diffracted electron beam intensity distribution is obtained which has a relatively low background level and a plurality of definite maximal values as shown in FIG. 3.
In the case where the measuring object is a material close to an amorphous material, a diffracted electron beam intensity distribution such as depicted by a solid line in FIG. 4 is obtained. In this case, the measuring object does not have many crystalline portions that satisfy the conditions of diffraction and the electron beams are mostly scattered by amorphous portions of the measuring object in unspecified directions; consequently, maximal values in the diffracted electron beam distribution are small and their peaks are broad. That is, the ratio of the inelastic or multiple scattering components, i.e. the above-mentioned background components, to elastic scattering components increases, and hence no sharp peaks appear in the diffracted electron beam intensity distribution. The broken line in FIG. 4 indicates the background components.
As described above, according to the prior art, when the measuring object has a crystal structure that is close to an amorphous structure, the ratio of the background components in the diffracted electron beam intensity distribution increases, and consequently, maximal values of the diffracted electron beam intensity distribution --a clue to clarification of the crystal structure--become indefinite. Hence it is difficult, in the prior art, to analyze the crystal structures of such materials.